The present invention relates to a vacuum producing system for pneumatically operated devices, and more particularly to a control system for a diaphragm vacuum pump drivingly connected to a prime power source such as a drive shaft of a vehicle engine to ensure operation of the pneumatically operated devices.
When the vacuum pressure necessary for a pneumatically operated device such as a vacuum brake booster for an automotive vehicle or the like is produced within the vacuum chamber of the device by reciprocation of a diaphragm vacuum pump, a large pressure difference exists between the sides of the spring loaded diaphragm piston of the vacuum pump in accordance with the increase of the vacuum pressure within the vacuum chamber of the device, thereby causing a heavy load to act on the diaphragm piston. Although the pneumatically operated device needs to be operated only in necessity, conveniently the diaphragm vacuum pump is constantly operated to ensure the operation of the pneumatically operated device when needed and it is thus exposed to the heavy usage which causes it to lose its durability and to shorten its life.